When you pull back the pool cover after winter, you might find a surprise. Instead of clear blue water, you see a green, dirty swamp. It's not fun to see, but don't worry—it's a common problem you can fix. This guide will show you the steps for how to clean a green pool and make it clear again. If you do it right and have some patience, you'll be swimming soon.
Step 1: Get the Pool Ready and Remove Trash
Before you add chemicals, you need to get the pool ready. This first cleanup helps the chemicals work a lot better.
First, use a strong leaf net to get all the big things out of the water. This means leaves, sticks, and anything else you see. This stuff uses up the chlorine you will add, so it's very important to get it out now.
Next, check your pool parts. Clean out the skimmer baskets and the pump basket. If a basket is full, water can't move well, and your chemicals won't mix in right. Also, make sure your filter is clean. If you have a sand or D.E. filter, backwash it. If you have a cartridge filter, take the cartridges out and clean them with a hose. Your filter is going to work hard, so it's good to start it off clean.
Step 2: Test and Balance the Water
You might want to just dump a lot of shock in the green water, but that's a bad idea. For the shock to work well, you need to fix the pH and alkalinity levels first. If the pH is too high, the chlorine won't work.
Use a good test kit to check your pH and total alkalinity.
- Total Alkalinity: Fix this first. You want it to be between 80 and 120 parts per million (ppm). Use a product to raise or lower it. Fix this first because it helps keep the pH steady.
- pH: After the alkalinity is good, fix the pH. You want it to be between 7.2 and 7.6. A lower pH around 7.2 will help the chlorine kill the algae even better. Use a product to raise or lower the pH to get it right.
Don't worry about the chlorine level right now. It's probably zero. Getting the pH and alkalinity right is the most important part before the next step.
Step 3: Shock the Pool to Kill the Algae
Now it's time to fight the green. Killing algae is called "shocking" the pool. This means you add a very large amount of chlorine to the water to kill the algae and other gunk. This is the main step for how to get rid of pool algae.
How Much Shock to Clear a Green Pool?
How much shock you need depends on how green the water is. This guide is for a 10,000-gallon pool. You should change the amount based on your pool's size.
- Light Green Water: If you can see the bottom, use a double dose of shock. This is usually 2 pounds of shock for every 10,000 gallons.
- Dark Green Water: If the water is cloudy and you can't see the bottom, use a triple dose. This is 3 pounds of shock for every 10,000 gallons.
- Very Dark Green or Black Water: If your pool looks like a swamp, you need to use a lot of shock. Start with a quadruple dose—that's 4 pounds of shock for every 10,000 gallons. You might need to add more later.
Always read the instructions on the shock package because the amount can be different. It is best to shock the pool at night. The sun burns up chlorine, so adding it at night lets it work for a long time. Keep your pump running for at least 24 hours after you add the shock so it mixes all through the pool.
Step 4: Run the Filter to Clear the Cloudy Water
After a day, you will see a big change. The pool won't be green anymore, but it will probably be cloudy and look milky blue or gray. This is a good sign! It means the algae is dead. Now you have to filter all the dead stuff out of the water.
Keep your pump running all day and night. Your filter is doing a lot of work, so you will need to clean it often. For sand or D.E. filters, backwash when the pressure is 8-10 PSI higher than normal. For cartridge filters, you might need to wash them with a hose every day until the water is clear.
If the water is very cloudy and you want to clean it faster, you can use a clarifier or a flocculant.
- Clarifier: This product makes tiny bits of dead algae stick together. This makes them big enough for your filter to catch. It works slowly, but it helps.
- Flocculant: This is a stronger chemical. It pulls all the dead algae into big clumps and makes them sink to the bottom. It works fast, but you have to vacuum the clumps up and send the water out of the pool, not through the filter. You will lose a lot of water this way.
Step 5: Brush and Vacuum the Pool
Chemicals and the filter do a lot, but you also have to do some work yourself to finish the job. Dead algae sticks to the pool walls, floor, and steps. Use a good pool brush to scrub every part of your pool. This knocks the dead algae into the water so the filter or vacuum can get it.
After you brush the whole pool, it's time to vacuum. If you used a flocculant, you have to set your filter to "waste" and vacuum the clumps from the pool floor. You will lose a lot of water, so have a hose ready to add more. If you didn't use flocculant, you can just vacuum like normal. But be ready to clean your filter right after because it will be full of dead algae.
At this point, a good automatic pool cleaner can be helpful. But it's usually best to do the first big vacuum by hand.
Step 6: Final Steps and How to Keep it Clean
When your water is clear, you are almost done. Now you need to test the water again for all the chemical levels. Check the chlorine, pH, alkalinity, calcium, and stabilizer. Change the levels so everything is in the perfect range for swimming. The full list of pool opening chemicals for a green pool includes chemicals to balance the water, shock to clean it, and now, chemicals to keep it clean.
Add a dose of algaecide to help stop the green from coming back. Now that the pool is clean and balanced, you can run your pump on its normal schedule. To ensure all that hard work doesn't go to waste and to prevent algae from returning, consistent, automated cleaning is your best strategy. This is where a powerful robotic cleaner like the iGarden Pool Cleaner K60 becomes invaluable. Its turbine-grade impeller and optimized flow system are designed to remove the fine debris that algae feeds on, while its Intelligent Path Optimization ensures every inch of your pool is scrubbed clean. Best of all, with one charge lasting the entire week, it turns the chore of daily maintenance into a truly hassle-free, set-and-forget routine.
